/**
*      author: Y_Yao
*      created: 2025-04-05 12:01:06
**/

#include<bits/stdc++.h>

#define int LL
using namespace std;
using LL = long long;
const LL LLINF = 9e18;
const int INF = 0x3f3f3f3f;
const int N = 1e5 + 7;
int n;
int a[N],b[N];


void solve()
{
    cin >> n;
    for(int i = 1;i <= n;i++)
    {
        cin >> a[i] >> b[i];
    }
    int ans = 0;
    for(int i = n;i >= 1;i--)
    {
        a[i] += ans;
        if(a[i] % b[i] == 0) continue;
        ans += b[i] - (a[i] % b[i]);
    }
    cout << ans << endl;
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int t = 1;
    // cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}
